1. Technical Field
The present invention relates to an alternating phase shift mask (PSM) used for fabricating semiconductor devices and a fabricating method of the same, and more particularly, to a wave guided alternating phase shift mask (WGAPSM) and a fabricating method of the same.
2. Description
Semiconductor devices having storage capacities of more than gigabits require a pattern with a design rule of less than submicron size. However, as the pattern size is reduced, a proximity effect occurs between adjacent patterns, lowering pattern resolution. In order to prevent the reduction of the pattern resolution, a phase shift mask (PSM) has been used which shifts the phase of a beam passing the mask to destructively interfere.
FIG. 1 is a sectional view of a conventional alternating PSM, and FIG. 2 is a graph of a substantial distribution of beam intensity when the PSM of FIG. 1 is used.
With reference to FIG. 1, an alternating PSM 10 includes a mask substrate 12, for example, a quartz substrate, on which an opaque pattern 14, for example, a chrome pattern, is formed to define a plurality of transparent regions A and B. The transparent regions A and B are formed of non-shift regions A, which do not shift the phase of incident beams, and shift regions B, which are formed by etching the substrate 10 for a predetermined depth to shift the phase of the incident beams. The beams passed through the non-shift regions A and the shift regions B have opposite phases and destructively interfere each other, so that the resolution of patterns, which are transcribed from the mask, is improved. Here, the intensity of the beams, which have passed the PSM, should be uniform at the non-shift regions A and the shift regions B. However, the intensity of the beams IB in the shift regions B is substantially lower than the intensity of the beams IA in the non-shift regions A, because the shift-regions B are formed by etching the substrate 12. When the beam passes through the shift-regions B that have defects on the surfaces of the substrate 12 due to the etching, the beam is scattered, thereby reducing the intensity of the beam. Specifically, the scatter of the beam at the rectangular corners of the shift-regions B mainly reduces the intensity of the beam. The difference in intensities generates an error CD of a critical dimension (CD) difference between adjacent patterns transcribed on a wafer. In addition, even if the error CD does not occur, an X-effect where the CD is reversed according to focus occurs when the beams fail to form a proper phase difference, such as 180 degrees, such as the case of FIG. 2 where defocus is 0.3 μm.
To solve the above problem, with reference to FIG. 3, another conventional alternating PSM 10′ forms preliminary shift regions B′ by etching portions of a substrate 12 on which an opaque pattern 14 is formed to set the phase of beams, which pass through the preliminary shift regions B′, to less than 180 degrees. Then, referring to FIG. 4, an isotropic etching process is performed to form shift regions B″ of undercut shape. Thus, the alternating PSM 10′ is completed as shown in FIG. 4. The main reason for scatter of the beam is overcome by the undercut, thereby preventing reduction of the intensity of the beam.
However, in the conventional alternating PSM 10′, chipping 16 in which portions of the opaque pattern 14 that are not being supported by the substrate 12, may break off, and the broken pieces of the opaque pattern 14 may operate as opaque defects 18. Moreover, as the pattern size is reduced, the margin for a wet etching process is reduced and the chipping is more likely to happen. Furthermore, since the etching amount is adjusted by controlling the wet etching process without using an etch stopper, a phase adjustment margin becomes very small.
To solve the above-described problems, it would be desirable to provide a wave guided alternating phase shift mask (PSM) to efficiently reduce an error CD and an X-effect, to avoid generating opaque defects in fabricating the PSM, and to secure a large phase margin.
It would also be desirable to provide a method of fabricating a wave guided alternating PSM.
In one aspect of the present invention, a wave guided alternating PSM (WGAPSM) that has a waveguide pattern for defining a transparent region is provided. The waveguide pattern is formed on the substrate to define a plurality of transparent regions that are regularly arranged. The transparent regions defined by the waveguide pattern include shift transparent regions formed of recess regions, and non-shift transparent regions alternatively arranged with the shift transparent regions.
The thickness of the waveguide pattern is preferably determined to guide the high order (i.e., having an order ≦−2 and ≧+2) Fourier components of wavefronts, which pass through the shift transparent regions, at least once, and more preferably, exactly once. The thickness is determined by a function depending on two independent variables, i.e., the wavelength of the exposure light source and the pitch size of the waveguide pattern, and the depth of the recess regions is determined by an equation of depth={wavelength of the exposure light source used for the mask/[2*(the refractive index of the substrate −1)]}.
It is more preferable that the wavelength of the exposure light source is less than 248 nm, the pitch size of the waveguide pattern is less than 1120 nm, and the thickness of the waveguide pattern is 4400 to 4600 Å.
It is preferable that the waveguide pattern is formed of a material having a transmittance of over 0% and less than 30% for the exposure light source.
It is preferable that the waveguide pattern defines a line and space pattern or an opening pattern in a cell array region of a semiconductor memory device.
In another aspect of the present invention, a fabricating method of a WGAPSM is provided. According to the fabricating method, a material layer for a waveguide pattern is formed on a substrate that is transparent to the light from an exposure light source. Thereafter, the waveguide pattern for defining a plurality of transparent regions is formed by patterning the material layer, and a resist pattern for exposing the transparent regions to be shift transparent regions is formed on the substrate. Next, the substrate is etched by using the resist pattern and the waveguide pattern as etch masks to form recess regions, so as to complete a plurality of shift transparent regions formed of the recess regions and a plurality of non-shift transparent regions alternatively arranged with the shift transparent regions.
Here, the thickness of the material layer is selected so to guide the higher order (i.e., ±2nd order; ±3rd order; ±4th order, etc.) Fourier components of wavefronts, which pass through the shift transparent regions, at least once, and preferably, exactly once.